1. Field of the Invention
The present invention relates to a method for monitoring the operation of optical supply line fibers within a transparent fiber-optic communications network, in particular according to patent DE 199 10 646.0, with at least two optical supply line fibers being provided for transmission of optical user signals between a central and a remote optical device.
2. Description of the Prior Art
In modern fiber-optic communications networks, in particular in communications networks using ring or double-star technology, the communications devices of a network customer of, for example, an Internet provider are connected to the fiber-optic communications network with the aid of a number of optical supply line fibers. Amounts of data in the Gigabit range are normally transmitted via such optical supply line fibers, with the data transmission taking place between a central device, for example a network node in the fiber-optic communications network, and a remote optical device, for example a network termination appliance. With such high data transmission rates, network customers demand that the network operator provide high reliability for the fully optical communications network and for the connection to the fiber-optic communications network.
In order to make it possible to ensure that the connection of the communications devices to the fiber-optic communications network is operating correctly, this connection must be monitored remotely. This means that information about the operational state of the optical supply line fibers for the respective network connection must be available in the respective network node. If, for example, a malfunction occurs for the connection of a network customer, then it is impossible for a network operator who is not remotely monitoring the connection of the network customer to assess whether the malfunction is located in his own responsibility area, for example because a digger has damaged one of the optical supply line fibers, or whether the fault is within the responsibility area of the network customer, for example his transmission laser is defective. It is, thus, advantageous to be able to monitor automatically and remotely whether defects and/or interruptions in optical supply line fibers are or are not in the responsibility area of the network operator.
Furthermore, in the case of fiber-optic communications networks which are being set up or extended, particularly in the case of metropolitan ring communications networks, the optical fibers or fiber pairs available for connecting the adjacent network nodes to one another are frequently not fully utilized between two adjacent network nodes, that is to say there is not yet any need for multiple use of the individual optical fibers by using wavelength division multiplexing (WDM) in an extension phase such as this or when the existing fiber capacities of the fiber-optic communications network are utilized at such a low level.
In conventional, known network architectures, it is possible to provide an unused optical fiber, which connects a number of network nodes to one another, exclusively for one network customer, via which the network customer can extract information from the fiber-optic communications network or can transmit to the fiber-optic communications network. Such optical fibers reserved specifically for one network customer are referred to in the specialist world by the term “dark fibers.” Dark fibers describes the fact that the optical signal transmitted in the optical fiber in the fiber-optic communications network is produced exclusively by the laser unit of the network customer and the optical signal received in the network node is not converted in any way by the network operator nor is it passed on, for example, once again at a different wavelength.
However, network architectures such as this provide the capability to provide a dark fiber only as an additional option to primary data transmission using WDM technology. That is, normally, optical supply line fibers for one network customer are passed to a WDM multiplexer which is located at a network node and using which the optical signals received via a number of supply line fibers are multiplexed onto a common optical fiber connecting the individual network nodes. In this context see, in particular, “A Cost-Effective Approach to Introduce an Optical WDM Network in the Metropolitan Environment”, S. Johannson, et al., IEEE Journal on Selected Areas in Communications, Vol. 16, No. 7, September 1998, page 1109 to page 1121. However, when a network customer is connected via such dark fibers it is impossible to monitor the transmission quality or to detect the transmitted amounts of data, as is required, for example, for the network operator to raise charges. No protective measures, for example alarming of the respective optical network node, have been provided either for the occurrence of a malfunction of the dark fibers in known communications networks, via which fault localization would be possible quickly and reliably. In addition, no protection circuits for dark fibers are known via which it would be possible to switch to the redundant optical dark fiber in the event of a fiber in the active optical dark fiber breaking. This lack of service facilities results in the network operator being able to connect only an extremely small number of network customers to the network via a dark fiber.
An object to which the present invention is directed is to improve the connection of network customers to the transparent optical fibers which connect the network nodes of the transparent fiber-optic communications network, in terms of both the monitoring of the optical supply line fibers and the reliability of the connection passed via the optical supply line fibers and, thus, to allow step-by-step extension of the fiber-optic communications network, initially without using WDM technology.